@Ramses_X Several months later, and apparently there's some contention on the suitability of Py-GC-MS specifically for reliably detecting micro and nano-plastics within high-fat tissues like the brain (or at least polyethylene specifically):

https://cosmicretreat.tumblr.com/post/775774049112571904 (yes, I was originally cued into this development from Tumblr; yes, I will use this incident as an excuse to continue to stay active on Tumblr)

Which leads to two folks on Twitter, both of whom appear to have experience in working with MNPs:

Dr Materic (https://x.com/DusanMateric/status/1886730304859062773)

With three contentions:

1. Figure S7 [which Dr Materic erroneously labels as Kidney rather than Liver, though his point would stand when comparing either kidney or liver to the brain] versus Figure S10 of Brain, both under light microscopy, showing many more readily apparent microplastics in equivalent areas for the liver/kidney than the brain, contradicting the authors' Py-GC-MS findings.
2. The flake-like nano-particles of the brain from Figure 2.d are too regular and unlike other nano-particles.
3. The high measurements of PE are indicative of false-positives due to fatty nature of brain tissue.

and Dr. Bergmann (https://bsky.app/profile/melaniebergma18.bsky.social/post/3lhg664zt6k27 ; could not find original twitter link, though this bluesky link mirrors the content; no, i will not (re)create an X account; yes, scientists need to get the fuck off of X), who also mentions possible unsuitability of Py-GC-MS findings for polyethylene in fatty tissue specifically:

>Super important methodological implications for studies on #microplastics in humans, which currently tend to overestimate microplastic levels if Pyrolysis–Gas Chromatography–Mass Spectrometry is used, especcially for fatty tissues.

by linking to the following paper:

https://pubs.acs.org/doi/10.1021/acs.est.4c12599

which claims that Py-GC-MS is not suited for measuring polyethylene in biological matrices:

>It was concluded that Py-GC-MS is currently not a suitable analysis method for PE and PVC in biological matrices due to the presence of interferences and nonspecific pyrolysis products.

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The authors of the original paper changed the abstract from the preprint (https://pmc.ncbi.nlm.nih.gov/articles/PMC11100893/) to the published version (https://pubmed.ncbi.nlm.nih.gov/39901044/) in order to imply that they also employed other methods (SEM-EDS) to double-check their work and rule out such false positives:

3c3
< Applying pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) methods to isolate and quantify MNPs from human samples, we compared MNP accumulation in kidneys, livers, and brains.
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> Complementary methods for the robust detection of tissue MNPs, including pyrolysis gas chromatography-mass spectrometry, attenuated total reflectance-Fourier transform infrared spectroscopy and electron microscopy with energy-dispersive spectroscopy, confirm the presence of MNPs in human kidney, liver and brain.

Specifically, Extended figures 6 and 7 show SEM-EDS data on brain samples that, from my limited understanding, purport to demonstrate that the particulates identified, at least in the specimens that underwent SEM-EDS, are *not* such false positives.

Later in the discussion, the authors explicitly mention possible issues with polyethylene in high-fat tissues within Py-GC-MS -- the (IMO) strongest contention that both of the scientists on Twitter/X/BlueSky make -- and make their case for why their methodology should be less susceptible to those issues; indeed, they argue that their polyethylene counts may well be underestimates (they also make a weak counter-argument to contention 2 by being hand-wavy about "well maybe these nano-fragments are hitherto unknown final byproducts of nanoplastic breakdown, suitable for absorption into brain tissue"):

>Lipids have been noted as a potential source of interference in Py-GC/MS analysis of PE[16]. Our method of KOH digestion and physical separation of solids was designed to reduce this concern, rather than augment it with a liquid–liquid extraction in organic solvents that would selectively drive lipid partitioning. Furthermore, the spectra suggest a reduction of longer carbon chains in the pyrolysis chromatogram, which is potentially due to advanced oxidative degradation of the MNPs and excess carbonyl formation that may lead to an underestimation of the concentration, as our standards are created with pristine polymers[17,18]. Finally, given the observed small size of nanoscale particles isolated from the human specimens (typically <200 nm in length), it is likely that ultracentrifugation incompletely collected nanoplastics in the analytical samples, also contributing to potential underestimation. The shape and size of observed nanoparticles in the isolated material from human specimens taxes the limits of modern analytical instrumentation but may reflect an end-stage product of plastic degradation that is uniquely suited for human uptake and accumulation.

And as for contamination, the authors basically argue that they were careful:

>Numerous quality control steps ensure that external contaminants are not impacting the results, including Py-GC/MS assessment of KOH and formalin storage control sample ‘blanks’ and measurements of the polymer composition of all plastic tubes and pipette tips that are essential in the digestion and measurement process (Supplementary Figs. 2–4). Decedent specimen collections over the past 30 years were not focused on minimizing external plastic contamination. However, given the consistent nature of handling and processing across all organ samples within objectively clean clinical and forensic settings, the significant accumulation of MNPs in the brain cannot be dismissed as an artifact of contamination. Furthermore, the 2016 samples were stored for 84–96 months compared to only 2–4 months for the 2024 samples, which exhibited greater concentrations of polymer. Thus, contamination from plastic storage vessels should not influence the conclusions.

Certainly sounds like replication could help determine just how careful they really were.

I'm definitely out of my depth here, but I'm curious and following along as best as I can. My gut tells me that, while the authors' SEM-EDS work likely does establish the presence of some MNPs in the brain tissue, the Py-GC-MS measuring technique for quantifying just how much is present might be suspect. Further, the authors' arguments against contamination, as I understand them, still rely on the reliability of Py-GC-MS to accurate quantify MNPs in samples (including their pristines and their blanks). If Py-GC-MS itself is not as suited to the task as thought, then those arguments likely don't hold weight, and so there could also be undetected contamination of the samples.

Yay science!